This invention relates to a drive system for a carding machine for processing textile fibers such as cotton or synthetic fibers and is of the type in which the fiber processing rolls situated in the zone of the doffer are driven by an electromotor coupled to an electronic motor control and regulating unit including desired value setters. A change of the output speed is effected, for example, by changing the rpm of the electromotor. The drive system is further of the type in which the draft (that is, the longitudinal tensioning force imparted on the running, coherent fiber material) is adjustable.
In an apparatus of the above-outlined type, disclosed, for example, in German Offenlegungsschrift (application published without examination) 29 44 428, the doffer is associated with a first motor control which includes an electronic tachogenerator, an electronic motor regulator and a variable speed motor which drives the doffer as well as the rolls which are situated in the doffer zone. The electronic motor regulator comprises an rpm regulator with a subordinated current regulator. A desired value setter (such as a potentiometer) for the output speed which corresponds, for example, to the rpm of the doffer, is connected with the electronic motor regulator with the intermediary of a desired value preselector. The first motor regulator for the doffer is connected by means of an electric shaft with a second motor control for the feed roller at the input of the carding machine. The second motor control includes an electronic tachogenerator operatively coupled to the feed roller, an electronic motor regulator and a speed variable motor driving the feed roller. A desired value setter for the feed roller (such as a potentiometer) for setting the draft, is coupled with the electronic motor regulator with the intermediary of a desired value preselector.
The electronic tachogenerator and the electronic motor regulator for the doffer are connected via a desired value preselector for the feed roller with the electronic motor regulator for the feed roller (electric shaft).
The output speed (for example, 150 m/min) equals the circumferential speed of the calender rolls behind the sliver trumpet or in the sliver coiler and is determined by the rpm of, for example, the doffer. The draft (for example, one hundredfold) equals the ratio of the circumferential speed of the calender rolls to the circumferential speed of the feed roll. The total draft is determined in the German Industrial Standard DIN 64080.
The total draft is composed of the product of several individual drafts, for example, of the draft between the calender roll pair and the doffer and the draft between the doffer and the feed roller.
In the known system in case of a new setting (for example, when a batch change occurs) a certain total draft, for example 100%, is set which is maintained during operation. For this purpose the potentiometer is used which is connected to the electronic motor regulator for the feed roller. At the same time, all individual drafts, for example, the draft between the calender rolls and the crushing rolls (for example 23%) are set which also remain constant during operation. In contrast to the draft, the output speed may change during operation. It ranges from the high peak velocity during production through the lesser velocity during the run-up or run-down phase down to the low delivery speed during the beginning phase of the fiber thread-in operation. During such a change of the output speed the initially set draft remains constant. Stated differently, even if the output speed changes, the draft--either the total draft or the individual drafts--remains constant. The feed roller and the doffer are connected to one another by an electric shaft and rotate synchronously at a certain ratio relative to one another.
To obtain high output speeds for achieving a high production rate, large drafts are required. If such large drafts are preserved even at low output speeds (for example, during the thread-in operation), the fiber web is ruptured on the rolls during the low output speed because the drafts for such a speed range is excessive. Such problems become increasingly more serious as the difference between the starting speed and the final speed of the card increases. This problem limits the peak velocity of the card and thus also limits the peak output rate.